The subject matter disclosed herein generally relates to pressure regulation in fluid flow systems, such as fuel flow systems.
In a fuel system for an engine, for example, an aircraft engine, a pressure regulating valve is utilized to deliver fuel at a selected pressure and mass flow rate to the engine by a controlling pressure drop across a fuel controlling valve. Excess fuel flow is bypassed. A typical pressure regulating valve 100 is shown in FIG. 7. The valve 100 includes a movable piston 102 biased toward a closed position (shown in FIG. 7) by a spring 104 and by pressure P2. Inlet pressure P1 urges the piston into an opened position against the bias of the spring 104. Fluid flow 106 flows in through a valve inlet 108 at P1 and out through valve outlet 110 at PD. A key feature of the piston 102 is neck diameter 112, and neck opening height 114 between piston 102 and cylinder 116. During valve operation, once the piston 102 travels such that an axial opening width 118 equals the neck opening height 114, the valve 100 reaches its saturation point, meaning that additional travel of the piston 102 will not help pass more flow through the valve, and the valve is effectively an orifice that loses the ability to control the pressure drop across the valve. To avoid saturation in valve design, the neck opening height 114 is typically increased, but this results in flow velocity at the valve outlet 110 to be decreased. With lower outlet flow velocity, it is difficult to balance forces in the valve 100 and such conditions also result in valve “droop”, pressure setting shift from the set point. Further, the neck opening height 114 must be sized to meet requirements at high flow and low pressure conditions (droop high limit). Thus, operation at high flow and high pressure conditions will increase droop in the valve 100.